I know it seems like a small thing, but I work with complex spreadsheets, and supporting coloured sheet tabs would really help 
Love this control.

Support scenarios where users can use the spreadsheet component to design templates with disabled cells.

I appreciate that this can be customized (as almost anything) but note this is the only cell property that is not configurable via the toolbar.

We are using the Kendo UI spreadsheet in a real-world website. We have a design team who are providing a visual design which fits in with our company's corporate standards.

HTML5 aims at separating styling from the layout design, which enables different teams to build the syle, with very little development experience, but more artistic experience.

For some reason, the Spreadsheet control can only be styled via the API (javascript code)! This means our design team needs to write their style in javascript, which is completely unrealistic.

It should be a fairly simple change to allow a range object to have a CSS class associated, and let HTML work like it should.

It would be useful if copy and paste the data have the option of fill the series or copy the value for the date format. 
Furthermore, copy from multiple column value and allow to paste multiple copied value from the spreadsheet will be added advantage. 

Thanks. 

DefaultCellStyle property in spreadsheet has a field “Wrap”, but doesn’t have a field “Format”. For example, if I need to process all cells as text, I must set the field “Format” on a client side:
sheet.range("A1:AX200").wrap(true).format("@");
It works.
But the initialization of the range ("A1:AX200") takes time… It is not very fast…
It would be better to have the field “Format” in the DefaultCellStyle property in spreadsheet…

Presently in Spreadsheet tooltip is not working for filter applied range 
so tooltip should display for each cell in which the range of filter is applied

Currently if you access cells range programmatically, you can set background color, text color etc.
It would be good to have the way to set classes or to get the DOM of the range.
Another option would be to get DOM or set a class to individual cells (e.g. via range.forEachCell).

Currently the spreadsheet dynamically creates the FilterMenu for a range, that is, it's not created until someone clicks the filter dropdown, and it's destroyed if they switched tabs.

There is no event that is fired when these things happen, which makes it hard to attach to, and customize, the FilterMenu without setting up some crazy listening code (setTimeout, etc.). 

It would be great if either (or both:
- You could specify a template for the filter menu.
- You could listen for a "FilterMenu Initialized" event and capture the menu there and customize it.

Custom editors are great!  But often when you have a custom editor, you want to restrict data entry to only use that editor, and not free-form typing in the cell.  You can prevent free-form typing in the cell by disabling the cell, but then the custom editor button is no longer available.

Suggestion is to still show custom editor button even if cell is disabled, perhaps with an additional setting; so that you could optionally not show the custom editor if the cell is disabled, since often a disabled cell should prevent any kind of modification.

I have a first example using the Kendo Toolbar widget and I was able to get an Angular button rendered in the toolbar:
http://dojo.telerik.com/ucIfin
When I tried to do the same thing in the Kendo Spreadsheet widget toolbar, it failed to compile my template:
http://dojo.telerik.com/UseWI

In general Angular directives are not compiled properly when specified in the template of a Spreadsheet Toolbar item.  I am aware of a workaround for the kendo-button specific case, but I would like the template to work for custom Angular directives as well.

In MS Excel when you type a number you can easily go to other cells by using the arrow keys and type in another number, thus allowing for fast editing of the spreadsheet. This does not work in the spreadsheet component.
this functionality only needs to work when not creating a formula.

I use data binding data source for spreadsheet
But when I use it, data auto input begins at row 0
I want to insert 2 row (To Write title)

The Excel file downloaded from Spreadsheet does not maintain leading spaces.  In other words, the internal sharedString.xml should use <t xml:space="preserve"> when necessary.

type =IF( "a"="A" ; 1 ; 0 ) and =IF( EXACT("a";"A") ; 1 ; 0 )
into Kendo Spreadsheet and Google Spreadsheet and MS Excel.
There is a special EXACT function (which is also available in Kendo) to enforce case-sensitivity. By default it should be off.

I have altered the kendo code to add row and column references to the k-spreadsheet-cell dom objects. A sample of this is: 
<div style="color: rgb(81, . . .  class="k-spreadsheet-cell r17c1 row-17 col-1"> . . . .
I have items that I wish to place on top of cells in the spreadsheet.
I can use these classes to identify the dom element corresponding to a spreadsheet cell object. I wish that this thing would let me post images. This is working really well. 
Request: It would be nice if the spreadsheet code to do this out of the box. Further, it would be beneficial to add a 'tag' property to a spreadsheet cell that would be indicated in the cell's dom object. If a cell has a tag, it should be rendered even if it doesn't have non-trivial formatting or a value.

IF any custom validation available for spreadsheet cells, then while exporting the sheet, those validation error messages or formats not getting exported. So here it will be helpful if its exports validations too. So user can see error in both UI and Exported file. 
In the below example, user can see the error messages in ui but cant see on the exported file. 
https://docs.telerik.com/kendo-ui/controls/data-management/spreadsheet/how-to/validation-to-column

I see some potential for improvements here, I see how the Spreadsheet entirely depends on the JSON structure. It doesn't have to be like this as the setDataSource() method shows clearly that the columns could be further configured: 

https://www.telerik.com/forums/datasource---specify-columns#msCK2ytWcESxeUMs-6a3uQ

Therefore, the Sheet columns could be configured upon the widget initialization. Such configuration options could be represented in the following manner for the HTML helper version of the widget:

.Columns<Kendo.Mvc.Examples.Models.SpreadsheetProductViewModel>(columns =>
{
    columns.Add(c => c.ProductId).Name("Product ID").Width(100);
    columns.Add(c => c.ProductName).Name("Name").Width(415);
})

Wanting to format a subset of a single cell with text styling different from the rest of the cell contents.  Something like the following:

or

Bug report

Client-side exported Excel workbooks are exported "uncompressed" (as readable text) and their size is much greater than the original document.

Regression since R2 2019 - 2019.2.514

Reproduction of the problem

1. Go to https://demos.telerik.com/kendo-ui/spreadsheet/index
2. Open the following file in Spreadsheet -
   Workbook Original.xlsx - 26 KB
3. Export the file to Excel

Current behavior

The exported file is 1015 KB in size. The content of the file may be read as plain text

Expected/desired behavior

The exported file is 26 KB or similar size. The content of the file is unreadable binary data

Environment

• Kendo UI version: 2019.2.619
• Browser: all